The invention is in the field of electronic reproduction technology and is directed to a light beam deflection unit in a scanner device for an apparatus for scanning masters or for a recording apparatus. Such a scanner device essentially comprises a light source for generating a light beam, a deflection unit for the light beam and an optical unit for correcting the light beam.
In a master scanning apparatus, also referred to as input scanner, a light beam generated in a scanner device is conducted point-by-point and line-by-line across an original to be scanned, and the scan light reflected from the original or allowed to pass therethrough is converted into an image signal in an optoelectronic transducer. In a recording apparatus, also referred to as a recorder, exposer or output scanner, the light beam for recording information acquired in a scanner device is intensity-modulated by an image signal and is conducted point-by-point and line-by-line over a light-sensitive recording material.
In the case of a flat bed apparatus, the holder for the master or for the recording material is a plane surface over which the light beam is conducted point-by-point and line-by-line, and that moves relative to the scanner device. In the case of an inside drum apparatus, the holder for the master or for the recording material is designed as a stationary half shell or trough. The scanner device moves parallel to the longitudinal axis of the holder, and the light beam is conducted radially across the master or the recording material perpendicular to the longitudinal axis.
An inside drum recording apparatus is disclosed, for example, by EP-A-0 354 028. The light beam deflection unit therein is designed as a mirror surface arranged transversely relative to the light propagation direction, and is connected to a shaft turning around a rotational axis. The rotating mirror surface deflects the light beam across the recording material point-by-point and line-by-line.
During operation of the recording apparatus, contaminants can collect at the mirror surface, and air turbulences can arise at high speeds due to the asymmetrical design of the light beam deflection unit with reference to the rotational axis. The air turbulences lead to disturbing noises and contamination in the region of the mirror surface. Beyond this, the air turbulences can exert alternating pressures on the bearing for the rotational axis that can cause slight shifts in the position of the mirror surface and, thus, of the deflected light beam on the recording material. Further, the optical path of the light beam in the light deflection unit can be influenced by the air turbulences, so that additional shifts in the position of the light beam on the recording material can arise. Such positional errors of the light beam lead to non-uniform exposures on the recording material, as a result of which the reproduction quality is disadvantageously deteriorated, given a high-quality recording apparatus.
DE-A-41 24 229 discloses a light beam deflection unit with a light entry face and a light exit face for the perpendicularly deflected light beam that is composed of a rotationally seated carrier prism and of a light-transmissive deflection prism that extends in the direction of a rotational axis. The face of the deflection prism adjoining the carrier prism is designed as a reflection surface that proceeds transversely relative to the rotational axis. The deflection prism is glued to the carrier prism, and the two prisms supplement each other, at least in regions, to form a unit that is symmetrical relative to the rotational axis. Disk-shaped cover elements that project beyond the unit in the radial expanse are arranged to the side of the unit.
Given this light beam deflection unit, the cover elements in fact result in slight air turbulences, dirt and unquiet running as well; however, the positional errors of the deflected light beam caused by air turbulence cannot be entirely avoided. Further, the manufacture of the cover elements is comparatively involved since they must be precisely manufactured and precisely centered at the unit.
DE-A41 30 977 discloses another light beam deflection unit that is composed of a transparent member designed as a spherical segment and of a carrier member that is likewise designed as a spherical segment and that is glued to the transparent member at the reflection layer. The transparent member comprises a light entry face, a reflection face and a light exit face. The unit formed of the transparent member and the carrier member is rotatable around an axis that resides perpendicular to the light entry face and comprises an outside contour that is dynamically balanced, at least with reference to the axis. As a result of the spherical design of the unit, this light beam deflection unit can in fact rotate at a relatively high speed without creating substantial running noises; nonetheless, air turbulences can occur, these likewise disadvantageously causing disturbing positional errors of the light beam.